1. Field of the Invention
This invention relates generally to the manufacture of seamless tubing, and more particularly to a small sized rolling and piercing mill.
2. Description of the Prior Art
There is a variety of prior art equipment for making seamless tubing and which includes rotary piercing in a machine which uses rolls to grip the stock and advance it through a piercing machine having a mandrel-mounted point ("plug") to pierce the center of the stock as the stock is driven through the machine. The equipment known to me is typically large and expensive, requires a lot of space, is harsh on the tooling involved, and is not readily adapted to comparatively low volume runs of particular sizes of tubing. Also there are machines shown in some prior art patents known to me as follows:
______________________________________ U.S. Pat. No. Inventor Date Issued ______________________________________ 3,695,076 Kocks 10/03/72 3,882,595 Reiley et al. 5/13/75 4,052,874 Yoshiwara et al. 10/11/77 4,212,178 Bretschseider 7/15/80 4,318,294 Yoshiwara et al. 3/09,82 4,409,810 Yamada 10/18/83 4,470,282 Hayashi 9/11/84 4,571,970 Moltner et al. 2/25/86 4,577,481 Staat 3/25/86 4,578,974 Pozsgay et al. 4/01/86 ______________________________________
It appears that most of these machines employ some processing, typically rolling, for various purposes following the piercing station. The additional steps require additional space in the processing plant. Also, some of the patents use "shoes" (shoes 12 and 12' and shoes 70 and 72' in the Hayashi patent, for example) to keep the workpiece properly positioned between the skewed driving rolls as those rolls advance the workpiece through the machine. In addition to the friction of the workpiece against the shoes, and the additional power required to drive the workpiece through the machine, the shoes tend to wear out and burn out, because the workpiece is at forging temperature during the piercing operation. Also, the piercing point is subjected to high loads, wear and temperature and must be taken off the arbor after each tube is pierced. The point must then be cooled externally. In addition, the pierced tube is removed from the mill with the arbor laying inside the tube. The arbor is then removed from the tube and cooled externally. Consequently, the piercing points must be replaced frequently. It is therefore an object of the present invention to overcome some of these problems associated with prior art equipment.